Biomedical subjects

Chunchun Zhang

Publications and source records attributed to Chunchun Zhang.

3 recordsLinked to original sources

PubMed2006

ABCG2 expression, function, and promoter methylation in human multiple myeloma.

We investigated the role of the breast cancer resistance protein (BCRP/ABCG2) in drug resistance in multiple myeloma (MM). Human MM cell lines, and MM patient plasma cells isolated from bone marrow, were evaluated for ABCG2 mRNA expression by quantitative polymerase chain reaction (PCR) and ABCG2 protein, by Western blot analysis, immunofluorescence microscopy, and flow cytometry. ABCG2 function was determined by measuring topotecan and doxorubicin efflux using flow cytometry, in the presence and absence of the specific ABCG2 inhibitor, tryprostatin A. The methylation of the ABCG2 promoter was determined using bisulfite sequencing. We found that ABCG2 expression in myeloma cell lines increased after exposure to topotecan and doxorubicin, and was greater in logphase cells when compared with quiescent cells. Myeloma patients treated with topotecan had an increase in ABCG2 mRNA and protein expression after treatment with topotecan, and at relapse. Expression of ABCG2 is regulated, at least in part, by promoter methylation both in cell lines and in patient plasma cells. Demethylation of the promoter increased ABCG2 mRNA and protein expression. These findings suggest that ABCG2 is expressed and functional in human myeloma cells, regulated by promoter methylation, affected by cell density, up-regulated in response to chemotherapy, and may contribute to intrinsic drug resistance.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2006

The X-ray crystal structures of human alpha-phosphomannomutase 1 reveal the structural basis of congenital disorder of glycosylation type 1a.

Congenital disorder of glycosylation type 1a (CDG-1a) is a congenital disease characterized by severe defects in nervous system development. It is caused by mutations in alpha-phosphomannomutase (of which there are two isozymes, alpha-PMM1 and alpha-PPM2). Here we report the x-ray crystal structures of human alpha-PMM1 in the open conformation, with and without the bound substrate, alpha-D-mannose 1-phosphate. Alpha-PMM1, like most haloalkanoic acid dehalogenase superfamily (HADSF) members, consists of two domains, the cap and core, which open to bind substrate and then close to provide a solvent-exclusive environment for catalysis. The substrate phosphate group is observed at a positively charged site of the cap domain, rather than at the core domain phosphoryl-transfer site defined by the Asp(19) nucleophile and Mg(2+) cofactor. This suggests that substrate binds first to the cap and then is swept into the active site upon cap closure. The orientation of the acid/base residue Asp(21) suggests that alpha-phosphomannomutase (alpha-PMM) uses a different method of protecting the aspartylphosphate from hydrolysis than the HADSF member beta-phosphoglucomutase. It is hypothesized that the electrostatic repulsion of positive charges at the interface of the cap and core domains stabilizes alpha-PMM1 in the open conformation and that the negatively charged substrate binds to the cap, thereby facilitating its closure over the core domain. The two isozymes, alpha-PMM1 and alpha-PMM2, are shown to have a conserved active-site structure and to display similar kinetic properties. Analysis of the known mutation sites in the context of the structures reveals the genotype-phenotype relationship underlying CDG-1a.

Amino Acid Sequence↗

PubMed2003

Synthesis, in vitro affinity, and efficacy of a bis 8-ethynyl-4H-imidazo[1,5a]- [1,4]benzodiazepine analogue, the first bivalent alpha5 subtype selective BzR/GABA(A) antagonist.

The synthesis and in vitro affinity of the alpha5beta3gamma2 (alpha5) subtype selective BzR/GABA(A) antagonist 7 is described. This ligand is selective for alpha5 subtypes in vitro and is a potent antagonist of the effects of diazepam only at alpha5beta3gamma2 subtypes (oocytes). Ligands such as 7 will be important in the determination of which physiological function(s) are subserved by this GABA(A) alpha5 subtype.

Animals↗